The objective of this project is to define the initial, intra-cellular events of steroid hormone action. Synthetic glucocorticoid derivatives, some of which could react to form covalently labelled receptors via affinity labelling, are being used with glucocorticoid-responsive rat hepatoma tissue culture cells to examine: (1) steroid-receptor binding site interactions; (2) the effects of steroid binding on receptor conformation; and (3) the nature of "activation" of receptor-steroid complexes. Fluorescence spectroscopy represents one technique for examining these interactions. Two series of synthetic steroids have been synthesized which potentially could give covalent, fluorescent receptor-steroid complexes via fluorescent chemo-affinity labeling. In another approach, we have incorporated the novel reactive functional group beta-hydroxy-alpha-keto-mesylate into cortisol to yield cortisol-mesylate, which appears to be the first long acting, and possibly irreversible, anti-glucocorticoid.